Antenna design principle

Recently saw a classmate in order to enhance the mobile phone GPS signal, the antenna DIY to the outside, pulled a very long antenna, their own in the suspicion that this is in line with the principle of antenna design, can really make the signal enhancement? So find the following article to learn.

 1. RFID Fundamentals        RFID (radio frequency identification) is an automatic identification technique for communication using radio waves. The basic principle is the data communication through the electromagnetic coupling or inductance coupling between the reading head and the label sticking on the object, in order to achieve the automatic identification of the label items. [1]-[5] Automatic recognition refers to the application of a certain identification device, through the identification of the object and identification device close activity between the automatic acquisition of the information of the identified items, and provide to the background computer processing system to complete the relevant subsequent processing of a technology. The complete automatic Identification system includes: Auto identification systems, aids;application interface, api;middleware; application software. The automatic recognition system can be divided into data collection technology and feature collection technology according to the characteristics of recognition object. RFID Chinese is generally translated into radio frequency identification technology, non-contact identification technology. The typical RFID system consists of the tag electronic tag (transponder) Reader Reader (reading head) and information processing system. The electronic label and reader are used to collect the information of the identified object, and the information processing system is used for control and processing. The hardware part of RFID mainly has two parts: Tag electronic tag (transponder) Reader Reader (reading head). Electronic tag tag can be divided into active and passive. The active tag is included with the battery, the identification distance is far, but the life limited price is higher and the volume is larger, generally active modulation. Passive electronic tags do not contain batteries, using the coupling of the reader to emit electromagnetic energy as their own energy, light weight, small size, long life, low price, but the launch distance is limited, the need for larger readers to provide energy. Generally passive modulation. The        RFID system can be divided into active, passive and semi-active according to different modulation modes. As a general rule, passive systems are reactive and active. The active system uses its own energy to send data to the reader actively, and in the case of an obstacle, the active mode of operation transmits the signal only through the obstacle once. The passive system uses the modulated scattering method to transmit the data, and must use the carrier of the reader to modulate its signal. Internal without battery, the typical energy-generating device is the antenna and the coil, close to the reader, the antenna receives a specific radio wave, the coil generates a current, through the rectifier circuit, activating the circuit switch. There is also a semi-active system between the two, also known as the battery-backed backscatter modulation system, the semi-active system label itself is also equipped with a battery, but does not actively send data, the battery is only used to power the internal digital circuit.The main bands of        rfid are: 125khz,134.2khz,13.56mhz,860-960 Mhz,2.45ghz and 5.8GHz. The working distance of RFID system with different working frequency is different, and the field of application also varies. Low frequency segment (lf,125khz,134.2khz) RFID system is mainly used for animal identification, factory data acquisition, etc. high frequency (Hf,13.56mhz) RFID system technology has been relatively mature, widely used in access control, intelligent transportation, etc. LF and HF frequency bands are used in inductive coupling mode, the general working distance is small. RFID system with UHF segment (uhf,860-960 MHz) The effective working distance can reach 3-6 meters, suitable for logistics, supply chain and other fields. Microwave frequency bands (2.45GHz and 5.8GHz) are used for container management and road tolls, and UHF and microwave frequency bands are applied in electromagnetic coupling to work far away.         At present, RFID has not yet formed a unified global standard. International RFID-related communication standards mainly include: EPC standard (mainly for HF and UHF bands), DSRC Standard (5.8GHz band) and a series of ISO standards: ISO/IEC 18000 standard (including 7 parts, involving 125KHz, 13.56MHz, 433MHz, 860-960mhz, 2.45GHz and other bands), ISO11785 (Low frequency), ISO/IEC 14443 standard (13.56MHZ), ISO/IEC 15693 standard (13.56MHZ). The current RFID system is mainly used in closed market management, such as control access to the access system, vehicle identification, highway charges, etc., the next step is to use electronic tags to replace the display of widely used barcode system, combined with the Internet to form an open logistics management network.  2. Design and application of RFID tag and reader antenna         RFID system antennas are generally divided into electronic label antenna design and reader antenna two categories. The antenna design of RFID system with different working frequency bands has its own characteristics. For LF and HF bands, the system uses inductive coupling, the work energy required by the electronic label is obtained by the coupling coil radiation of the reader, which is generally passive system, the working distance is smaller than 1 meters. In the Near field of the reader is not actually involved in the problem of electromagnetic wave propagation, antenna design is relatively simple. For UHF and microwave frequency bands, the electronic label is generally located in the far field of the reader antenna, the working distance is far. The reader's antenna provides the electronic labelAs energy or wake-up active electronic label, UHF frequency band is passive working system, Microwave frequency band (2.45GHz and 5.8GHz) is mainly semi-active mode of operation. Antenna design has great influence on system performance. For UHF and microwave band electronic label antenna design, the main problems are: I. Antenna input matching        UHF and microwave band RFID antennas are generally used in the form of microstrip antennas. In the traditional microstrip antenna design, we can control the antenna size and structure, or use impedance matching converter to make its input impedance match the feeder, the better the antenna matching, the better the antenna radiation performance. However, due to the cost of the electronic label antenna can only be directly connected with the label chip. Chip impedance is often characterized by strong weak resistance, and it is difficult to measure the exact impedance characteristic data of the chip in operation. In the design of electronic label antenna, it is difficult to match the input impedance of the antenna with the chip impedance. While maintaining the performance of the antenna while the antenna and the chip match. This is a major difficulty in the design of electronic label antennas. II. Antenna direction map         electronic label, in theory it is hoped that it can receive the energy of the reader in all directions, so it is generally required that the label antenna has omni-directional or hemispherical coverage directionality, and requires the antenna to be circularly polarized. Iii. the effect of antenna size on its performance         Due to the small size of the electronic label antenna, its input impedance, direction map and other characteristics are susceptible to processing accuracy, the effect of dielectric board purity. In strict control of the size of the antenna also requires a considerable gain, the greater the gain, the greater the electronic label working distance.         The current application of electronic label antenna is basically the use of patch antenna design, the main form of microstrip antennas, such as line antenna. In recent years, electronic label antenna design has been a hot spot in RFID systems [6] [7]. The label Antenna study focuses on how to achieve wideband characteristics [8][9][10], impedance matching [11], and the article relates to the effect of the antenna backplane on label performance [12]. Reader antennas generally require the use of directional antennas, can be divided into two types of combined and sub-assembly. Fitting means that the antenna and the chip are integrated together, the sub-assembly is the antenna and the chip through the coaxial line, in general, the reader antenna design requirements than the label antenna is lower. Recently, there has been a study on the reader antenna using the smart antenna technology to control the direction of the antenna main beam, increase the reader can cover the area [13].  3. The department in the RFID tag antenna design advantages and disadvantages          from the previous article, electronic label antenna development of the entire RFID system has a very importantMeaning, it also has a certain degree of difficulty. At this stage, although there are a large number of professional antenna design manufacturers, but very little involved in RFID System electronic label antenna design. There are still some gaps in the design of the label antenna in the microwave band, and the vast majority of foreign designs involve patent issues. If the resources are put forward in advance, the development of products with self-intellectual property rights can not only fill the domestic blank but also effectively break the monopoly of foreign products and promote the establishment of relevant domestic standards.         The department has been devoting considerable resources to the development of Microstrip antennas, in the past there have been a number of studies around the application of microstrip antennas and theoretical analysis, but also has the relevant experimental equipment can be used for the development and design of microstrip antennas, for the development of electronic label antenna has a considerable basis. The department has several network analyzers that can be used to measure the impedance of a label antenna, or to measure an antenna's direction map. The deficiency of this department lies in the emphasis on scientific research theory and design, and the ability of scientific research innovation to transform into enterprises is weaker.  

Principle of antenna design